1. Field of the Invention
This Invention relates to an industrial process efficiency method and system and relates particularly to a method and system for improving the efficiency and performance of any industrial process that uses motor-driven pumps to move liquids, slurries, gases and other fluid or fluid-like material. The invention has particular application in the field of heating, ventilation and air-conditioning systems (HVAC) used, for example, for comfort conditioning for buildings. More specifically, the present invention is directed to methods and systems of improving the overall operating performance and efficiency of movement of fluids such as in HVAC systems.
While the invention has broad application throughout all areas of industry, such as in cool rooms, paper processing, water and/or sewage treatment plants, or any other system that incorporates fluid pumping and the like, for simplicity and ease of understanding the invention, it will be described herein in relation to its use in HVAC systems. It will be understood, however, that the invention is not limited to its use in such systems.
2. Description of Related Art
Compression type HVAC systems and direct expansion air conditioners are the most commonly used cooling systems for buildings nowadays. HVAC systems and direct expansion air conditioners operate by absorbing heat from the space being cooled either directly (direct expansion air conditioners) or by circulating a secondary fluid (e.g. water or air). Rejecting the heat that has been absorbed and has been generated by the cooling apparatus is accomplished almost universally by transferring the heat to the environment outside the building or space.
Known systems typically have a motor which drives a compressor drawing low pressure refrigerant gas from an evaporator and discharging it as a higher pressure hot gas into a condenser. In the condenser, the hot gaseous refrigerant is condensed into a high pressure liquid refrigerant which flows through an expansion device that regulates the flow of refrigerant into the evaporator. The low pressure refrigerant absorbs heat of vaporization from the chilled water or air circulating through the evaporator, and low pressure refrigerant vapor is drawn back into the inlet of the compressor and the cycle is continuously repeated.
Usually such cooling apparatus has some method of regulating cooling capacity for part load operations, such as a modulating scroll or vane apparatus which limits the amount of refrigerant through the compressor, or a variable speed apparatus which controls the rotational speed of the compressor, or both. The chilled water/hot water or chilled air/warmed air is generally circulated through a distribution system for comfort conditioning within the building.
In typical systems, the heat absorbed from the evaporator, along with the heat added by the compressor, is transferred to the external air through the condenser, preferably using cooling towers or the like.
When water is being chilled by the evaporator to about 4.4 to 10° C., it is then delivered by a chilled water pumps to the cooling load, which may include water cooling coils in terminals in which air is cooled and dehumidified.
In the prior art, several arrangements are used for connecting water chillers into chilled water supply and distribution systems. Further, several arrangements are used for condenser water cooling. However, all systems proposed previously suffer from inefficiencies when loadings vary from optimum design loadings.
For example, when cooling loads drop during part-load operation, the water volume flow rate of the plant loop (primary chilled water circuit) keeps in constant flow and maintain in full capacity which is recommended by all chiller configuration guidelines due to their awareness that any reduction of water flow rate in the primary water circuit may adversely affect the efficiency of chiller, and may further lead to the instable operation of the chiller. In this connection, all prior arts which attempt to operate the primary chilled water pump at reduced speed in accordance with the load which will lower the water flow rate of primary chilled water circuit with respect to its original constant flow rate arrangement is not recommended by the chiller's manufacturers.
With regard to the secondary chilled water circuit (also known as building loop), when cooling loads drop during part-load operation, the water volume flow rate reduces in the building loop because control valves have been partially closed. The water pump, therefore, is caused to operate at a loading less than full capacity and therefore at less than maximum efficiency. In prior art, someone may use a variable speed drive to operate the secondary chilled water pump at reduced speed in accordance with the load, however the water flow rate of the secondary chilled water circuit is lowered too. And the extent of energy saving is not significant when compared with our present invention.